Different dimensions, but all same weight?

[Songbirdo]

UPDATED:

I was wondering how coins of different dimensions can contain the same amount of silver?

Using the dimensions from this source:
http://www.golddealer.com/about_silver_bullion.html

US Silver Eagle
Diameter: 1.598" (Approx 40.6 mm)
Thickness: 0.117" (Approx 2.97 mm)

Canadian Mint
Diameter: 38 mm
Thickness: 2.87 mm

Aussie Philharmonic
Diameter: 37 mm
Thickness: 3 mm

Finding the volume of a cylinder (these are short cylinders) is the area of a circle times its thickness.
Area of a circle is pi*r^2 (r=D/2)
Volume of a cylinder is pi*r^2*t

Volume of American Silver Eagle: 3845.02 mm^3
Volume of Canadian Mint: 3254.91 mm^3
Volume of Aussie Philharmonic: 3225.63 mm^3

The silver eagle is much larger than the other two mints. How is this possible?

The reason I'm asking is I got a walking liberty coin from Goldenstate Mint and mistook it for a silver eagle. I realized it didn't have a mint date on the front and then compared it to the tube of silver eagles I'd gotten a while back. That's when I discovered it wasn't a silver eagle, but a mimic coin from another mint. When I placed the coin on top of the silver eagle, I found the eagle was slightly larger in diameter.

Does the silver eagle have non-silver components? Or could this be because it's squished in the center more pushing more silver outward? shown in the image below.
http://i1206.photobucket.com/albums/bb44...inking.png
Unfortunately I have yet to obtain any other mint's coins than these two, so I have not a third party to compare to.

The Goldenstate coin has stamped on it "1 troy ounce" ".999 fine silver".
http://i1206.photobucket.com/albums/bb44...iberty.png
The Silver Eagle only has "1 oz fine silver."
http://upload.wikimedia.org/wikipedia/co...of_Rev.png

Then I did a "ring" test on both coins, as well as the 90% peace dollar, and 90% walking liberty half dollar. The Eagle, the peace dollar, and the walking liberty half all resonated brilliantly, holding their chime throughout their entire flight. Getting a ring was effortless. On the Goldenstate Mint... it was very difficult to get any chime, and when it did it faded quickly.

Makes me wonder if the Goldenstate mint coin isn't 100% silver as it claims to be...?

Any insights on the size discrepencies and the goldenstate mint coinage?